Contact lens options for keratoconus - Optometry Today

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Contact lens options
for keratoconus
Course code: C-15460 O/D/CL
45
Dr. Narendra Kumar, BAMS, PGCR, Member IACLE
Keratoconus is a bilateral, usually asymmetrical, non-inflammatory disease
of the cornea. It is characterised by progressive corneal thinning and apical
protrusion (Figure 1). It presents in early adulthood and visual symptoms
result from irregular astigmatism and increasing myopia. 1 Usually, the
protrusion affects the axial and inferior nasal cornea. There is decreasing vision
associated with the ensuing distortion and glare, and this does not improve
in advanced cases with spectacle correction. There are several non-spectacle
options available for the correction of keratoconus, from simple contact
lenses to surgical approaches, an overview of which is presented in this article.
Keratoconus management options for
today’s practitioners include spectacles,
soft contact lenses, rigid gas permeable
fitted flat so that it would stay on the
cornea. Due to the flat fit, it wasn’t
very comfortable for the patient but
(RGP) contact lenses, piggyback decidedly better than a soft lens in
systems, hybrid contact lenses, INTACS,
corneal collagen cross-linking (CXL),
keratoplasty, Rose-K lenses, Nissel K2
rigid lenses, Kerasoft IC lenses, and
scleral contact lenses. With such a
range of options now available, for all
severities of the disease, optometric
practitioners need to be aware of how
best to manage their patients. Indeed,
terms of providing good vision. Today’s
variation, the availability of RGP 2 as
a spherical lens, is a healthier option
because of better oxygen transmission to
the cornea. Furthermore, technological
advances mean that manufacturing of
soft and RGP spherical lenses and toric
lenses can make use of modern computer
numerical controlled (CNC) lathes to
spectacle correction may well provide produce custom-designed specialty
useful vision in some mild cases of
keratoconus, as may soft contact lenses,
especially of the thicker lathe-cut variety
and toric designs, but advanced cases
will require more specialist approaches,
some of which can be provided from
contact lenses, which are a necessity
for progressing cases of keratoconus. 3
RGP fittings are usually done from a
trial set or ordering empirically from
the “K” readings (keratometer reading)
along with the spectacle refraction and
community optometric practice. back vertex distance (BVD). The total
RGP lenses
The yesteryears’ rigid contact lens was
a spherical polymethyl methacrylate
(PMMA) material, which was usually
lens diameter (TD) may be around
9.50mm, with the BOZR matching the
flattest “K” or being “two thirds of the
way towards the flattest K”. Since the
lens is rigid, having a sharp edge, it
Figure 1
Outward bulging cornea in keratoconus
needs to be handled with care so as not
to traumatise the cornea at the time of its
insertion in the eye. Upon removal, the
technique can follow a simple ‘pull and
blink’ method, as used in the days of
PMMA lenses, which tends to work well
especially with keratoconic corneas. 4
RGP lenses are available in spherical
designs and in an array of different
materials with varying Dk values. Whilst
considered an excellent modality for
the management of mild to moderate
keratoconus, they have unfortunately
decreased in popularity, with more
than 90% of contact lens fittings
constituting that of soft lenses, due
to their ‘easy-fit-and-forget’ approach
(even by unqualified or under-qualified
practitioners in some countries such
as India 5 ). There are not very many
practitioners dealing in RGP contact
lens fitting, and they may naturally
enjoy the benefit of referrals from those
dealing only in soft contact lens fitting.
Piggyback system
For cases of non-tolerance to RGP
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Figure 2
Hybrid lens from SynergEyes
contact lenses, it is possible to use a
piggyback system whereby a RGP lens
is fitted over an underlying soft lens;
the latter provides both comfort and
stability. A reverse piggyback system
may also be thought of in some cases,
if it results in better vision. Indeed,
in either case, with the availability of
super-Dk silicone hydrogel and RGP
lens materials, the use of the piggyback
system has become better in terms of
enhanced oxygen availability to the
cornea and reduced risk of complication.
For lens care, using a single soft lens care
product usually suffices although in the
case of reverse piggyback, a specific
RGP lens cleaner may be advisable.
Piggybacking a RGP lens over a soft
lens can convert an unsuccessful contact
lens fit into a successful one, particularly
in keratoconus. Choosing a soft lens
power of plano to –0.75DS, which has
a front surface nearly parallel to the
back surface, won’t dramatically alter
the shape to which the base curve of the
RGP lens is being fitted. In fact, when
commencing the contact lens fit, the RGP
lens base curve may be selected based
on keratometry values taken over the
soft lens worn on the cornea. Sometimes
the soft lens power may be manipulated
to alter the surface on which to place
the RGP lens. For example, a soft lens
of power -5.00D when fitted over a very
steep keratoconic cornea provides a
flatter, more stable surface upon which
to place the RGP lens. Likewise, a soft
lens of power +5.00D will steepen the
fitting surface over an extremely flat
post-Radial Keratotomy (RK) cornea. 6
Hybrid contact lens
Hybrid contact lenses consist of a
high-Dk RGP centre and a soft skirt
(Figure 2); the former portion provides
good vision whilst the latter provides
stability and comfort on the eye. The
SynergEyes KC lens is a hybrid design
that has a RGP centre made of Paragon
HDS 100 (Dk 145) material and a
skirt made of 27% water hydrophilic
material. The diameter of the rigid
central portion is 8.4mm and the total
diameter of the lens is 14.5mm. The
curvature of the posterior portion of the
RGP is described as a ‘prolate ellipsoid’.
The lens tends to remain stable on
the eye of a patient with keratoconus,
without decentering on horizontal or
vertical eye movement, since the soft
skirt provides stability by centring
the optics of the lens over the pupil.
Rose-K lenses
The back surface of the Rose-K contact
lens for keratoconus is a series of
spherical cuts that are well blended;
these are produced by software-guided
computerised lathe. Fitting is done
using a diagnostic set. The first trial
lens chosen is 0.2mm steeper than the
average “K” reading. A local anaesthetic
may be used to reduce tearing for
quicker and accurate fluorescein
Figure 3
Optimum fit immediately after blink
assessment; a minimal amount of
fluorescein should be instilled so as
not to disrupt the tear film and also
so that it doesn’t lead to inaccurate
assessment of the pooling patterns.
First of all, central fit is assessed for
a light feather touch at the apex of the
cone and the rest of the pattern as close
to an alignment fit as possible (Figure
3). The peripheral fit is assessed next;
the trial lenses have a standard edge
lift, but an increased or decreased
edge lift on the same base curve can
be ordered. Lens diameter is assessed
next; the standard diameter is 8.7mm,
but smaller diameters of 8.1mm to
8.3mm work well on steeper corneas,
and a larger diameter may be required
for early cones. Assessment of
power is done last by over-refraction
with the contact lens in situ. 7
Nissel K2 rigid lens
Available in a wide range of base
curves, diameters and edge lift
options, the Nissel K2 rigid lens
(Cantor & Nissel Ltd.) is manufactured
from Optimum Extra (Contamac)
as standard, with other materials
available. The total diameter of the lens
is 8.7mm as standard (other diameters
being 8.1mm, 8.4mm, 9.0mm, and
9.3mm). All trial lenses are single use,
removing concerns about disinfection.
Corneal topographers are ideal, but if
a keratometer is used then the average
of the flattest and steepest “K” readings
are calculated, and the first trial lens
is selected as having a base curve as
close as possible to 0.30mm steeper
than the average “K” value. The aim
is to obtain good visual acuity (VA) in
a lens that is comfortable. The ideal
fit exhibits good centration, having
minimal clearance or light touch at
the area of the cone, combined with
good alignment over the cornea,
with a band of edge clearance

0.50mm to 0.80mm wide.
sclera (Figure 4).
The fitting sets are supplied
The lenses trap a
with each base curve having
reservoir of fluid
a standard value of edge lift;
behind
them,
the axial edge lift can be
which
protects
increased or decreased. If
the cornea, and
the lens is riding high then
it is advised that you select a
smaller diameter lens, and if
the lens is riding low then it is
advised that you select a larger
diameter lens. Full sphere
/ cylinder over-refraction
should then be conducted
to arrive at the correct
contact lens power, taking
account of BVD corrections.
Although the central cornea
in keratoconus can indicate
significant corneal toricity,
the peripheral cornea is often
spherical, and the best VA may usually
be achieved with a spherical optic zone. 8
Kerasoft IC lenses
The term ‘rigid’ appears shocking to
many would-be contact lens wearers
and practitioners alike. Equally, the
notion of a ’soft lens for keratoconus’
comes as a welcome relief to such
persons. The lathe-cut silicone hydrogel
or non-silicone hydrogel high-water
high Dk Kerasoft IC lens (Ultravision
Ltd.) comes in base curves from 7.40mm
to 9.40mm, diameters of 14.0mm to
15.5mm, in a front surface asphere or
asphere toric prism ballasted form, with
Figure 4
Scleral lens cross section
vision and comfort; until now, this was
only possible with RGP lenses but can
now be achieved with a silicone hydrogel
material too. Consequently, the lens
provides comfort, stable vision and longer
wearing time even in a dry environment. 9
Scleral contact lenses
Large diameter (14.0mm to over
20.0mm) RGP lenses that completely
cover the cornea and extend onto the
sclera are known as scleral lenses.
They are supported exclusively by the
because of their
size they rarely
dislocate from
the eye. They
mask corneal
irregularity in
keratoconus (and
other conditions
like keratoplasty
and post-refractive
surgery), and
are particularly
useful for patients
who need visual
correction but are
unable to wear other types of contact
lenses. 10 These are so-to-say modern-day
transformation (in high-Dk material) of
the older-time haptic lenses that were
used in 1959. An example of a scleral
lens is the Boston lens, a proprietory
scleral contact lens now known as
PROSE (Prosthetic Replacement of
Ocular Surface Ecosystem) since it is
used as a prosthesis for conditions of
corneal ectasia including keratoconus. 11
INTACS
INTACS are thin plastic semi-circular
rings that can be inserted into the cornea.
47
25/02/11 CET
periphery options of standard, steep,
steep (reverse geometry) and flat. A
wide power range is available (+30.00
DS, cylinder -0.50D to -15.00D and axis
1 o to 180 o ) and fitting is done from a trial
set of lenses with standard periphery
and plano power, with over-refraction
conducted. The Kerasoft IC lens offers
Sector Management Control (SMC),
which allows individual customisation
of the lens periphery to enhance fit,
Figure 5
Intacs corneal rings
Figure 6
Intacs imbedded in the cornea

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They were originally used as a
form of refractive surgery for the
correction of low myopia but are
now used for cases of keratoconus
(Figures 5 and 6). The surgical
procedure using local anaesthetic
drops and a clamp to hold the
eye still involves the placing of
inserts just beneath the surface,
in the anterior stroma, in the
peripheral cornea. By inserting
the semi-circular rings in this
manner, INTACS can flatten
the cornea, changing the shape
and location of the cone and
eliminating some of the corneal
irregularities in keratoconus.
Improvement in vision is
certainly notable, but spectacles
or contact lenses may still be needed.
INTACS improve contact lens
tolerance in patients with keratoconus,
as well as improving best-corrected (and
uncorrected) VA, whilst also delaying
the need for surgical treatment by
keratoplasty (see later). The peripheral
circumferential corneal elevation
above the ring segment inserts creates
mechanical barriers when fitting rigid
contact lenses, thus reducing RGP lens
sensation; however, semi-scleral contact
lenses have no corneal bearing at all and
can work even better. If soft contact lenses
are selected instead, there is no additional
problem posed, and if astigmatism has
been reduced and/or becomes more
regular, makes fitting even simpler. 12
Corneal collagen cross-linking
Corneal collagen cross-linking (CXL)
results in stiffening of the corneal stroma
through photochemical cross-linking of
the collagen fibres, resulting in a denser
network of bonds and increased stability
of the cornea. After epithelium ablation,
Riboflavin drops are applied and the
cornea is then exposed to ultraviolet
(UV) light of wavelength 365nm. The
Figure 7
Keratoplasty steps
procedure is performed under local
anaesthesia. After the treatment a
bandage contact lens is applied and
a steroid-antibiotic combination
drop is prescribed. Post-operative
contact lens fitting becomes more
tolerable and results in stable VA with
minimal long-term corneal stress. 13
Keratoplasty
Perhaps as a last resort, a corneal
transplant is required when the cornea
becomes dangerously thin or when
VA cannot be improved with contact
lenses due to steepening or scarring of
the cornea, or due to lens intolerance.
During the day-care surgery, the diseased
or injured part of the cornea (termed
the “button”) is removed and replaced
with a clear donor tissue “button”,
and is fixed into place with sutures
(Figure 7). A patch and shield are then
applied to the eye to protect it until the
surface epithelium heals, usually in
1 to 4 days. Post-operative care as per
ophthalmologist’s recommendation is
extremely important, and includes use
of steroid drops; proper care and prompt
attention to any sign of rejection of the
graft will need to be dealt with but
otherwise hopefully the graft
remains clear and healthy. 14
Summary
New Delhi recently witnessed
an excellent educational
session on contact lenses for
keratoconus and irregular
cornea with eminent speakers
including Dr. Paul Rose (Rose
K lenses), Ken Pullum (Scleral
lenses), Lynn White (Kerasoft
IC lenses), Jyoti Dave Singh
(Piggyback system) and Monica
Chaudhry (Lens care solutions).
The message that came out loud
and clear was that there is a
plethora of choices from simple
spherical soft and RGP contact lenses,
to specialty contact lens options, that
can be utilised by eye care practitioners
for the management of keratoconus in
order to provide their patients with
excellent stable vision and comfort
before the need for surgical intervention.
About the author
Dr. Narendra Kumar holds a Diploma in
Optometry (DROpt), degree in Ayurvedic
Medicine and Surgery (BAMS), the
Certificate in Rehabilitation (PGCR) and
is a member of IACLE. Having served as
Refractionist at Sir Ganga Ram Hospital
for 30 years, he now looks after contact
lens cases at his ophthalmologist son’s
clinic OphthaCare Eye Centre. He
has been editing the quarterly journal
Optometry Today (India) since 1970,
is the chairman of the charitable trust
Eye Care India, and the author of
‘Ophthalmic Dispensing Optics’ and
‘Babloo goes for an eye test’ books.
References
See http://www.optometry.co.uk/
clinical/index. Click on the article title
and then download “references”

Module questions
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Course code: C-15687 O/D
1. Which neurological stream should visual fields assessment
primarily assess in AD and PD?
a) Parvo-cellular system
b) Konio-cellular system
c) Magno-cellular system
d) None of the above
2. What is the expected “awareness of practitioner” for a person with
accommodative flexibility of 10cm fixating a practitioner at 3 metres?
a) Neck
b) Chest
c) Waist
d) Hips
3. What is the likely postural problem if a person with visual midline
shift perceives a fixation rod in front of their right eye when in fact it is
in front of their nose?
a) They have an upright posture
b) They have a turn to their left
c) They have a turn to their right
d) They are leaning backwards
4. The Motion Displacement test may prove useful for assessing AD
and PD patients as it assesses:
a) Magno-cellular function
b) Motion coherence processing
c) Parvo-cellular function
d) Static coherence processing
5. Which of the following statements about glaucoma in patients
with AD or PD is FALSE?
a) Patients should have more frequent visual field tests
b) Patients should be assessed with threshold visual field methods
c) They have a greater risk of accelerated visual field loss
d) None of the above
6. Which of the following statements about AD and PD is FALSE?
a) Retinal OCT and photography will be increasingly important in the future
b) Cataract extraction is contraindicated
c) Single vision spectacles should be dispensed instead of varifocals
d) Objective tests may be more appropriate than subjective tests
Course code: C-15460 O/D/CL
1. What is the main characteristic feature of keratoconus?
a) It is a bilateral condition
b) It is a non-inflammatory condition
c) It presents with hypermetropia and irregular astigmatism
d) There is central infero-nasal corneal protrusion
2. What is a hybrid contact lens?
a) It is a dual material lens with a RGP centre and a soft periphery
b) It is a dual material lens with a soft centre and a RGP periphery
c) It is a RGP lens with plasma treatment for enhanced surface wettability and
comfort
d) It is a silicone hydrogel material combined with PMMA
3.Which of the following is NOT an appropriate management option
for keratoconus?
a) RGP contact lens
b) Corneal collagen cross-linking
c) LASIK
d) All of the above
4. What differentiates a corneal contact lens from a scleral contact
lens?
a) Corneal lenses mask irregularity in keratoconus but scleral lenses do not
b) Corneal lenses have a reservoir of tear fluid behind the lens but scleral
lenses do not
c) Scleral lenses will display central corneal touch but corneal lenses will not
d) Scleral lenses are supported wholly by the sclera but corneal lenses are not
5. After which keratoconic treatment may a contact lens correction
still be required?
a) Keratoplasty
b) INTACS
c) Corneal collagen cross-linking
d) All of the above
6. Which of the following is the MOST widely used treatment for
moderate cases of keratoconus?
a) Keratoplasty
b) RGP contact lens
c) Soft contact lens
d) Corneal collagen cross-linking
49
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